Pebble Bed Modular Reactor

1. Pebble Bed Modular Reactor Eric Glatstein, May 8, 2003

2. Pebble Bed Modular Reactor • nuclear fission reactor • uranium or thorium fueled • graphite “moderated” • high temperature operation • helium cooled • small, “modular” construction • intrinsic safety

3. Electrostatics “+” and “–” charges like charges repel opposite charges attract

4. Plum-pudding Since atoms evidently are electrically neutral, + / - charges must be uniformly distributed.

5. Rutherford scattering (c.1911) (Really Marsden and Geiger.)

6. Rutherford scattering “+” concentrated in smallvolumes

7. So, what’s holding “nucleus” together against “+” electrical repulsion?

8. So, what’s holding “nucleus” together against “+” electrical repulsion? Strong Nuclear Force

9. The New Physics • Niels Bohr (1913) • hypothesizes quantized angular momentum • Erwin Schrödinger (1925) • describes electron orbits with “wave equation” • Werner Heisenberg (1927) • ties it all together with the “indeterminacy principle” • Karl Llewellyn (1930) • describes the law with quantum jargon

10. Neutrons • James Chadwick (1932) • in addition to positively charged “protons,” nuclei contain neutral “neutron” particles. • together, called “nucleons.”

11. Atomic mass N Z neutron number, N, v. proton number, Z

12. Missing mass

13. Missing mass H The weight of a nucleus is less than the sum of its parts. U Fe

14. Stability Nuclei (like everything else) try to approach lowest energy level: lowest point on graph light nuclei undergo “fusion” heavy nuclei undergo “fission” Missing mass released from “Binding Energy” between nucleons. (E = m c2 )

15. Fission • Otto Hahn (1939) • bombarded uranium with neutrons • light “fragments” and heat unexpectedly appear • more neutrons out than put in • energy largely released as “Kinetic Energy” (gets Hot)

16. Neutrons “Fast” and “Slow” Most emitted neutrons travel too fast to cause another uranium fission: do not remain near nucleus long enough to cause instability For self-sustaining “chain” reactions, a “moderator” is need to slow emitted neutrons. • light -- transfer momentum • low neutron absorption

17. Self-sustaining “chain” reactions • Oklo, Gabon, 1.7 – 1.5 BYBP • Chicago, Illinois, 61 YBP (1942) Enrico Fermi (1st artificial)

18. Common moderators • Graphite • Hydrogen-2 (deuterium; “heavy” water) • Hydrogen-1 (“light” water) • Boron

19. Useful materials Atomic Energy Act of 1954 42 U.S.C. § 2014.  Definitions. (z) The term "source material" means (1) uranium, thorium, or any other material which is determined by the Commission . . . to be source material; or (2) ores containing one or more of the foregoing materials, in such concentration as the Commission may by regulation determine from time to time. (aa) The term "special nuclear material" means (1) plutonium, uranium enriched in the isotope 233 or in the isotope 235, and any other material which the Commission . . . determines to be special nuclear material, but does not include source material; or (2) any material artificially enriched by any of the foregoing, but does not include source material.

20. “Fissile” materials 23592U(naturally occurring at ~ 0.7% ) t½ = 700 million yr 23392U(effectively zero in nature) 10n + 23892U 23992U 23993Np 23994Pu t½ = 24 min t½ = 2.4 day t½ = 24,000y 10n + 23290Th 23390Th 23391Pa 23392U t½ = 22 min t½ = 27 day t½ = 160 thous yr

21. Coolants • Air • O2 can support corrosion / combustion • Carbon dioxide • Water • “light” and “heavy” • Liquid metals, e.g., sodium • Inert gases, e.g., helium • good heat transfer • no corrosion

22. Nuclear “reactor” (“batch” configuration)

23. Reactor control • control rod withdrawal and insertion • reactivity “poisoning” at higher temperatures

24. Pressurized Water Reactor

25. Pressurized (Light) Water Reactors USS NAUTILUS (SSN-571) Launched: January 21, 1954 Byron Generating Station Operating license (first unit) granted: 1985

26. Optimism . . . “Our children will enjoy in their homes electrical energy too cheap to meter.” Lewis L. Strauss, Chairman, Atomic Energy Commission, September 16, 1954.

27. Cynicism . . .

28. Problems for reactors to overcome . . . • hard to build and operate well • “run-away” danger • radioactive leaks • waste / proliferation risk • low temperature; low thermal efficiency • output not easily dispatchable • outages necessary for regular refueling • uranium-235 is rare • people make mistakes • still waiting for the waste repository . . .

29. Benefits . . . • near zero greenhouse emissions (at least from generating stations) • Burn-up decommissioned bomb materials • maintain an electrical generating mix

30. Policy . . . • Appropriate regulation • set rigorous standards • enforce standards consistently • let new technologies thrive or die on their own

31. Hard to build and operate well The Nuclear Regulatory Commission believes that standardization of nuclear power plant designs is an important initiative that can significantly enhance the safety, reliability and availability of nuclear plants [and encourages] . . . plant designs which: -- Are essentially complete in both scope and level of detail; -- Cover plant design, construction, and quality assurance programs; -- Satisfy regulatory requirements before construction begins; and -- Can be referenced for individual plant applications. 52 FR 34884, September 15, 1987

32. Hard to build and operate well (cont.) Experience has shown that the "one-of-a-kind" approach to reactor design, construction, and operation has led to an operating reactor population of great variability and diversity, even among reactors from the same vendor. * * * This variability has introduced significant differences in the licensing and operation of these plants, in the transfer of experience from one reactor to another, in technical specifications, in operating procedures, and in backfitting considerations. Thus . . .10 CFR PART 52 — EARLY SITE PERMITS; STANDARD DESIGN CERTIFICATIONS; AND COMBINED LICESNSE FOR NUCLEAR PLANTS

33. March 24, 2002DONOR WON PRAISE IN ENERGY REPORT By DON VAN NATTA Jr. WASHINGTON, March 23 In Chapter 5 of Vice President Dick Cheney's [May 2001] national energy report, executives of the once-moribund nuclear power industry were probably thrilled to read that the White House supported "the expansion of nuclear power in the United States as a major component of our national energy policy." * * *One such proposal was the development of a new nuclear reactor designed to produce electricity -- a gas-cooled reactor built on tennis-ball-size graphite spheres -- that the report said "has inherent safety features." * * *

34. Cont. Exelon, the nation's largest nuclear energy company, is the only American corporation developing a design for the pebble-bed reactor, which it says will lead to a new generation of cheaper, smaller and more efficient nuclear reactors. The company says the pebble-bed reactor will be safer, too, though environmentalists in the United States and in other countries have sharply disputed this, calling the pebble-bed reactor a failed system vulnerable to terrorist attack. * * *The administration's endorsement of Exelon's technology was learned through interviews and documents provided to The New York Times by the corporation itself. * * *Exelon provided The New York Times with two documents that the company submitted to the task force that had not been made public by Mr. Cheney: a pamphlet describing the pebble-bed reactor and a one-page description of the reactor's benefits.The document begins, "Exelon Corporation believes that we have found a technology that possesses the characteristics necessary to successfully compete in a deregulated environment in the P.B.M.R., a design under development in South Africa."The document argues that the reactor is "safe, economic and clean."

35. “Pebble Bed Modular Reactor” (“plug flow” configuration)

36. Reactor interior (AVR reactor)

37. “Pebble” fuel elements

38. “Pebble” fuel handling • AVR reactor • 360,000 “pebbles” in core • 120 day detention • 15 cycles

39. Fuels PBMR developed for Thorium cycle (Germany 1967) Similar HTGR configuration operated with uranium PECO Peach Bottom unit 1 (Lancaster, Pa.) (1967 - 1974)

40. Proponents Each pebble self-contained Fuel stable to 2,800°C “Design basis” 1,600°C accident Releases limited from one “module” No need for “defense in depth” No need to cool pebbles before disposal Opponents Manufacturing defects Graphite burns Keep the “defense in depth” Pebbles large relative to fuel rods Safety

41. “Bomb grade” fuels • Highly enriched uranium (80% 235U) • 500 tons of HEU from 30,000 dismantled Russian nuclear weapons to be blended to “proliferation-resistant” low-enriched uranium (LEU) by 2013. • Mixed Oxide (“MOX”) • DOE believes that half of 100 ton plutonium stockpile is excess of military needs.

42. “Light Water” / “Pebble Bed”

43. Thermodynamic efficiency Hot Cool work TC TH Effmax = 1 - ——

44. April 16, 2002 Exelon Generation Not Proceeding with PBMR Exelon Generation has announced today that it will not be proceeding with Pebble Bed Modular Reactor (PBMR) project beyond the completion of the current feasibility study phase. Exelon Generation has advised PBMR Pty (Ltd.), the entity managing the project, that it will continue to devote technical personnel and executive leadership to the project for the time being. As of June 30, 2002, Exelon Generation’s support of the project will total about $20 million. Exelon recently conducted its regular review of investments to ensure a disciplined strategy focused on the fundamentals of generation, power marketing and distribution. Becoming a reactor supplier is no longer consistent with Exelon’s strategy.

45. Conclusions . . . • Probably safer • Probably cheaper • It would be nice to beat the swords into plowshares • Time will tell